1. Field of the Invention
The present invention generally relates to a short turning radius steering linkage based on the so-called Ackerman Steering Principal in which all wheels rotate on a circle with a common center; an improved linkage that is particularly well suited for use with front-wheel-drive wheelchairs.
Front-wheel-drive wheelchairs provide good tracting, dynamic stability, and accurate steering control. Although not limited to such applications, this invention is particularly well adapted for use as a steering system for front-wheel-drive wheelchairs.
2. Description of the Prior Art
The following patents relate to short turning radius steering systems.
U.S. Pat. No. 4,515,380, to Schumacher, discloses a steering linkage that has unequal angles of turn for two-steerable wheels of a vehicle. Each wheel is turned through a gear. While driving one or each of the gears by means of a steering drive element in the same direction of rotation, the positive engagement of the two gears through the pinion and the eccentric mounting of the pinion on the swing arm produce a larger angle of turn of the wheel running inside the turn as compared to the angle of turn of the wheel running at the outside of the turn.
U.S. Pat. No. 4,195,858, to Goodacre, discloses a steering linkage for a pair of wheels with upright pivot axes comprised of links and pivots. Torque can be applied to each wheel via a pivotal connection to an intermediate link when control links are pivoted about their fixed pivots by a drive applied through a tie bar. Each wheel can be rotated about its pivot axis by at least 180.degree., and the turning circles of the wheels have a common center which, when the wheels are steered describes a line parallel to the line which joins the pivot axes of the wheels. In a four-wheeled vehicle the described line is coincident with the rotational axes of the second set of wheels.
U.S. Pat. No. 2,368,142, to Kelley, discloses a wheelchair having large front wheels mounted on fixed axles, and a pair of smaller steered rear wheels. The two rear wheels are linked together via cams and a chain mechanism for turning the rear wheels at different angles. The patent describes turning of the rear wheels so that their axes intersect along the line corresponding with the axis of the front wheels. When the intersection point is disposed midway between the front wheels, the turning radius is at a minimum.
These prior art proposals have not proven to be altogether satisfactory in terms of their operation and/or economy of implementation.